As wireless computing and distributed sensor networks become more mature and widespread, a remaining issue for the technology deployment becomes the power source. Conventionally, a wireless, portable sensor or microprocessor is powered by a battery. Though battery technologies have improved, energy densities and lifetimes are still issues for many systems. A battery holds a finite amount of energy and when that energy has been consumed by its load, the battery must be recharged. For many remote systems, recharging a battery is not an option. If a system is required to remain idle for months or years and then spring to life at a certain moment, a battery may have already become depleted due to leakage or self-discharge.
Embodiments of the present invention provide power to (inter alia) small remote systems through the conversion of ambient environmental accelerations, i.e. vibrations, into electrical energy. Two vibration classes of interest are sinusoid and random, either or both of which may predominate in a given vibration environment. The basis for vibration-based energy harvesting in this work is velocity damped resonant generation (VDRG), where environmental accelerations are harnessed to drive a cantilevered mass into oscillation and energy is then extracted from the mass motion through damping forces. The damping forces can be created by the piezoelectric transduction mechanism that converts mechanical to electrical power. The piezoelectric effect provides high power density and simplicity in implementation across the micrometer to centimeter size-scales.
A number of different piezoelectric energy harvesting approaches have been described. See for example, Anton et al., “A review of power harvesting using piezoelectric materials (2003-2006)”, Smart Mater. Struct. 16 (2007) R1-R21, which provides an overview of work conducted in vibration harvesting, mechanics, efficiency, power storage and circuitry.
Despite the breadth of research into vibration energy harvesting, with a number of ad hoc designs being generated over sizes scales ranging from the micro to macro, issues remain which must be addressed before it can be effectively implemented in real-world applications including the need to maximize harvester power output performance with respect to volume. The present invention provides a solution to these problems in the form of novel energy harvesting devices comprising a plurality of planform-tapered piezoelectric beams that allow maximal power density for virtually any harmonic or random vibration environment. Applications where piezoelectric energy harvesting can be desired include; air, water and land-based vehicles, oil rigs, heavy machinery, bridges and other architectural structures subjected to vibrations. The terms “vibrational energy converter”, “vibrational energy harvester”, “energy harvester”, and “mechanical vibration to electrical energy converter” are interchangeable in the context of this specification.